WO2018162841A1 - Method and device for detecting conditions conducive to the onset of pumping with a view to protecting a compressor of an aircraft turbine engine - Google Patents

Abstract

A method and device for detecting conditions conducive to the onset of pumping that can affect a low-pressure compressor of an aircraft turbine engine, said turbine engine further comprising a high-pressure compressor, said method comprising: - a first step (E10) of measuring a speed variation (dV) of said aircraft; - a second step (E20) of measuring a speed variation (dN2) of said high-pressure compressor; a preliminary step (E30) of measuring an altitude (A) of the aircraft; the conditions conducive to the onset of pumping being detected when the following conditions a), b) and c) are jointly obtained: a) said speed variation (dV) measured over a predetermined time interval corresponds to an acceleration greater than a first positive threshold (S1); b) said measured speed variation (dN2) corresponds to a deceleration less than a second negative threshold (S2); and c) said altitude is greater than a third predetermined threshold (S3).

Description

 METHOD AND DEVICE FOR DETECTING CONDITIONS FOR PUMPING TO PROTECT A COMPRESSOR

 AN AIRCRAFT TURBOMACHINE

Background of the invention

The present invention relates to the general field of aircraft turbomachines. In particular, the present invention relates to the detection of pumping conditions that can affect a compressor of an aircraft turbomachine, in particular a low-pressure compressor of a double-body and dual-flow turbojet engine. In the present patent application, pumping conditions are understood to be conditions conducive to the occurrence of pumping. By definition, pumping is aerodynamic instability of the fluid flow through a turbomachine compressor, which may be accompanied by a flow reversal. For example, if the compressor is trying to compress more gas than the downstream turbine can deliver, there may be pulsed returns of hot gases to the front, that is, upstream of the compressor. the flow of gases, with stalling of the flow on the compressor blades.

Pumping can thus lead to damage to the constituent parts of a turbomachine. This damage includes the breaking of compressor blades, the destruction of bearings, or the extinction of the turbomachine. The importance of reliably and accurately detecting the conditions conducive to the occurrence of pumping in a turbomachine compressor is therefore understood in order to prevent it. The occurrence of pumping can indeed lead to operational consequences that can involve significant financial costs.

Means are known for preserving the integrity and performance of a compressor under certain conditions conducive to pumping. In particular, there are known methods and devices for detecting a risk of pumping in a compressor when the operating line of said compressor becomes lower. at a predetermined threshold, said pumping line. It is known in particular from the patent publication US4756152A a method of regulating the control of bleed valves in a compressor, in particular during a deceleration of the turbojet, in order to recover the margin pumping.

It is also known from patent publication FR 2 332428 A1 a blocking detector and a blocking detection method in a gas turbine engine. Some low pressure compressors for aircraft turbomachines, also known as boosters, have a relatively low pumping margin at high altitude. In other words, the line of operation of the compressor stabilized at high altitude is close to the pumping line. A low-pressure compressor of a double-body and dual-flow turbojet can therefore have an increased sensitivity to pumping over a certain elevated altitude. This requires a good control of the management of the protections against the pumping of the screw compressor. with respect to the transient phases that the turbomachine can see. In addition, the known methods and detection devices do not detect the conditions conducive to the occurrence of pumping in certain flight situations. An example of a problematic flight situation is that of an aircraft flying in so-called "auto-joystick" mode. When an aircraft undergoes a sudden increase of the headwind, the speed seen by the aircraft, which is measured relative to the relative wind, increases accordingly. In what follows, we will talk about the speed of the aircraft as the speed seen by the aircraft, measured for example by a Pitot tube anemometer. In auto-joystick mode and in the majority of the cruising phase of the aircraft, the power of the turbomachine is regulated so that the speed of the aircraft remains constant. Thus, during an increase in the headwind, the auto-joystick mode reacts so as to reduce the absolute speed of the aircraft, so that the speed seen by the aircraft remains constant. For this, for certain engine categories and depending on the control logic adopted by the engine, the auto-lever mode controls the reduction of the operating speed of the low pressure compressor (also called the N1 speed) of the engine. turbomachine, to reduce the speed of the fan of the turbomachine and therefore its thrust. This can be problematic for the detection of the pumping conditions, since the variations of the speeds of the turbomachine are limited by the self-lever mode, which prevents the usual means of detecting the pumping conditions from operating.

 There are therefore some conditions conducive to the occurrence of pumping, in particular conditions that may occur in the context of an altitude cruising flight, which can not be detected by the detection methods known to the state of flight. the technique.

Obiet and summary of the invention

An object of the invention is to propose a method for detecting conditions favorable to the occurrence of pumping, for protecting a low-pressure compressor of a double-body and dual-flow turbojet engine, particularly in the context of a Cruise flight in altitude.

Correlatively, another object of the invention is to propose a device for controlling the opening and closing of discharge valves of a double-body and dual-flow turbojet engine when conditions are detected that are favorable for the appearance of pumping a low pressure compressor of said turbojet engine.

Correlatively, another object of the invention is to provide a double-body turbofan engine with a low-pressure compressor is protected in case of detection of conditions conducive to the occurrence of pumping.

In the present description and the appended claims, the expression "greater than" is used to designate a quantity whose value is greater than or equal to another, while the expression "less than" is used to designate a quantity of which the value is smaller or equal to another. In addition, calculating a difference between a first quantity, for example a quantity measured at a first instant, and a second quantity, for example a quantity measured at a second instant, denotes the subtraction of this second quantity by this first quantity.

It will also be understood that a speed can be expressed in meters per second or Mach number. The Mach number of an aircraft is obtained by dividing the speed of this aircraft by the speed of sound, the speed of the sound being equal to 340 m / s in the air at a temperature of 15 ° C.

A first aspect of the invention thus relates to a method for detecting conditions conducive to the occurrence of pumping that can affect a low-pressure compressor of an aircraft turbomachine, said turbomachine further comprising a high-pressure compressor, said method characterized in that it comprises:

 a first step of measuring a speed variation of said aircraft;

 a second step of measuring a variation in speed of said high-pressure compressor;

 a preliminary step of measuring an altitude of the aircraft;

the conditions conducive to the occurrence of a pumping being detected when the following conditions a), b) and c) are carried out jointly:

 a) said variation in speed measured over a predetermined time interval corresponds to an acceleration greater than a first positive threshold, said first threshold being for example equal to 0.001 Mach per second, said time interval being for example equal to 10 seconds,

 b) said measured speed variation corresponds to a deceleration lower than a second negative threshold, said second threshold being for example equal to -8 revolutions per minute per second, and

c) said measured altitude is greater than a third predetermined threshold, said third threshold being for example equal to 25000 feet (7620 meters). Advantageously, this method allows the detection of conditions conducive to the occurrence of pumping reliably without affecting the operating parameters of the turbomachine. Advantageously, this method makes it possible to avoid the erroneous detection of conditions favorable to the occurrence of a pumping occurring due to phenomena producing effects similar to those of a variation in the operating speed of a compressor of the turbomachine, for example. for example, a decrease in this regime caused by a malfunction, by the absorption of ice or a foreign body, or by the appearance of other unstable phenomena such as a rotational detachment.

Advantageously, this method makes it possible to detect the occurrence of reliable pumping when the aircraft is flying at high altitude.

In a particular embodiment of the invention, the detection method further comprises:

 a fourth step of measuring a first controlled speed of the low pressure compressor;

 a fifth step of measuring a second current regime of the low-pressure compressor;

the conditions conducive to the occurrence of pumping being detected, independently of the fulfillment of conditions a), b) and c), when the following condition d) is realized:

 d) the difference between said first measured controlled speed and said second measured current regime is less than a fourth threshold, said fourth threshold being for example equal to -100 revolutions per minute. Advantageously, this method allows the detection of conditions conducive to the occurrence of pumping when the aircraft flies in auto-joystick mode.

In a particular embodiment of the invention, if the measured altitude is lower than the third threshold, the first and second measurement steps are ignored and the conditions favorable for the occurrence of a pumping are detected when the condition d) is realized.

In a particular embodiment of the invention, the detection of conditions conducive to the occurrence of a pumping triggers a command opening of discharge valves located between the low pressure compressor and the high pressure compressor.

In a particular embodiment of the invention, said variation in speed is measured by calculating the derivative of the regime and then filtering it with a time constant adapted to average the measurement over a time interval of between 1 second and 3 seconds. Another aspect of the invention further relates to a device for detecting conditions conducive to the appearance of pumping that can affect a low-pressure compressor of an aircraft turbomachine, said turbine engine further comprising a high-pressure compressor, said characterized in that it comprises:

 first means for measuring a speed variation of said aircraft;

second means for measuring a variation in speed of said high pressure compressor;

 third means for measuring an altitude of the aircraft;

 the device further comprising means for detecting an acceleration of the aircraft, said detection means comprising:

 means for activating a first indicator representative of a variation of speed;

 means for activating a second indicator representative of a variation in the speed of the high-pressure compressor;

 means for activating a third indicator;

 - Means for activating a pumping risk indicator representative of the detection of conditions conducive to the onset of pumping;

said pump risk indicator being activated when the first indicator, the second indicator and the third indicator are activated simultaneously;

the first indicator being activated when the variation in speed measured over a predetermined time interval corresponds to an acceleration greater than a first threshold, said first threshold being for example equal to 0.001 Mach per second; o the second indicator being activated when the measured speed variation corresponds to a deceleration lower than a second threshold, said second threshold being for example equal to -8 revolutions per minute per second; and

 o the third indicator being activated when the measured altitude is greater than a third predetermined threshold, said third threshold being for example equal to 25000 feet (7620 meters).

Advantageously, this device allows the detection of conditions conducive to the occurrence of pumping from the use of means conventionally used during the monitoring of the flight phases of an aircraft, which makes it simple to implement .

In a particular embodiment of the invention, the detection device further comprises:

 fourth means for measuring a first controlled speed of the low pressure compressor;

 fifth means for measuring a second current regime of the low pressure compressor;

 the means for detecting an acceleration of the aircraft further comprising means for activating a fourth indicator, the indicator being activated when the first indicator, the second indicator and the third indicator are not activated simultaneously and when said fourth indicator is activated, said fourth indicator being activated when the difference between said first measured controlled speed and said second measured current regime is less than a fourth threshold, said fourth threshold being for example equal to -100 revolutions per minute.

Another aspect of the invention relates to a turbomachine comprising a detection device according to the invention.

In the present description and the appended claims, it is considered that any magnitude of a predetermined value is within a range of including this value, the limits of this interval being able to move away from several orders of magnitude of this value.

Thus, the first threshold is between 10-Mach per second and 10 ^{~ 2} Mach per second, this first threshold being for example equal to 0.001 Mach per second.

The time interval is between 3 seconds and 20 seconds, this time interval being for example equal to 10 seconds. The second threshold is between -2 revolutions per minute per second and -20 revolutions per minute per second, this second threshold being for example equal to -8 revolutions per minute per second.

The third threshold is between 20000 feet (6096 meters) and 30000 feet (9144 meters), this third threshold being for example equal to 25000 feet (7620 meters).

Brief description of the drawings

The invention and its technical characteristics will be better understood on reading the description which follows, accompanied by several figures respectively representing:

 - Figure 1 shows, in section, a turbomachine on which the invention is applicable;

 FIG. 2 represents, in flowchart form, the main steps of a method for detecting conditions favorable to the appearance of a pump according to the invention, in one embodiment of the invention;

FIG. 3 represents, in flowchart form, the main steps of a method for detecting conditions favorable to the appearance of a pumping according to the invention, in another embodiment of the invention

FIG. 4 represents, in flowchart form, the main steps of a method of detecting conditions that are favorable for the appearance of a pumping according to the invention, in another embodiment of the invention

FIG. 5 represents, in flowchart form, an example of means of a device for detecting conditions favorable to the appearance of pumping, in one embodiment of the invention;

 - Figure 6 shows, in graphical form, an example illustrating the variation of several parameters representative of conditions conducive to the occurrence of pumping may affect a turbomachine on which the invention is applicable.

 Naturally, to meet specific needs, a person skilled in the art may apply modifications in the following description. Although it refers to various embodiments, the present invention is not limited to these specific embodiments, and any modifications specific to the scope of the present invention may be considered obvious to a person skilled in the art. the art of the corresponding technique.

DETAILED DESCRIPTION OF THE EMBODIMENT The invention therefore proposes, in order to detect certain conditions that are favorable to the occurrence of pumping that can affect a low-pressure compressor of an aircraft turbomachine, to monitor on the one hand this aircraft via detecting a variation in its speed, and also monitor the speed decreases of a high pressure compressor of the same turbomachine. As mentioned previously, an acceleration of the aircraft is an increase in the speed seen by the aircraft, and can therefore be caused by an increase in the headwind.

In addition, the invention proposes to improve this detection in certain flight situations by monitoring the altitude of the aircraft, in order to detect in particular pumping conditions specific to a flight above a certain threshold. altitude. In addition, a monitoring of the operating mode of the low pressure compressor vis-à-vis the controlled speed can also be implemented by the invention, in particular to detect pumping conditions below the aforementioned altitude threshold.

In other words, the invention proposes to identify and combine several indicators relating to the behavior of the turbomachine and the aircraft carrying the turbomachine, in order to reliably and selectively identify conditions conducive to the appearance of a pumping.

In the context of the present invention, it will be understood that an aircraft flies in a given flight phase. A flight phase of an aircraft is, for example, a takeoff phase, a climb phase, a descent phase, a landing phase, or a cruise flight phase.

In particular, it will be understood that the present invention is applicable to an aircraft flying in a high altitude cruising flight phase, during which the piloting of the aircraft is in auto-joystick mode.

FIG. 1 represents a sectional view of a turbomachine on which the invention is applicable. The turbomachine is here a turbojet T double body and double flow, mounted on an aircraft.

In general and unless otherwise indicated, it will be defined here that the front and the rear of the turbojet engine T, as well as the inlet and the outlet of said turbojet engine T, are defined relative to the direction of flow of the fluids within that -this. Therefore, the front and the rear of the turbojet are located respectively upstream and downstream of the fluid flow.

The turbojet engine T comprises a n-boat. The n-boat N surrounds all the components of the turbojet engine T, and comprises, for example, a fairing to protect these components from the outside. The nacelle N has an external structure which defines with an internal structure one or more veins V. This or these veins V allow the flow of a fluid, for example a flow of air, inside the nacelle N of the turbojet engine T. The turbojet engine T comprises a fan S mounted at the front of the nacelle N. The fan S is for example a rotor consisting of blades and / or blades, which is driven by the turbine of the turbojet engine T. The fan S has the function of to receive all the fluid that enters the front of the turbojet T, and to redirect this fluid in all the veins V of the nacelle N. The fluid received by the fan S is divided into a primary flow F1 and a flow secondary F2, respectively. The primary flow F1 passes through an inlet compressor, said low-pressure compressor CBP, formed inside the turbojet T and secured to the fan S. The role of the low-pressure compressor CBP is to increase the pressure of the fluid passing through it. A turbine engine T according to one embodiment of the invention further comprises a high pressure compressor CBP, a combustion chamber CC, a high pressure turbine THP and a low pressure turbine TBP. As illustrated, it will be understood that the high pressure compressor CHP is disposed at the rear of the low pressure compressor CBP. The high pressure turbine THP is disposed at the rear of the high pressure compressor CHP and the combustion chamber CC, and the low pressure turbine TBP is disposed at the rear of the high pressure turbine THP.

The low pressure compressor CBP is mechanically coupled to the low pressure turbine TBP by a first shaft A1, while the high pressure compressor CHP is mechanically coupled to the high pressure turbine THP by a second shaft A2 coaxially traversed by the first shaft A1.

The function of the CHP high pressure compressor is to receive and compress the gases from the low pressure compressor CBP.

The low-pressure compressor CBP and the low-pressure turbine TBP rotate at the same rotational speed, while the high-pressure compressor CHP and the high-pressure turbine THP rotate at the same speed. As illustrated, the double-body, dual-flow turbojet engine comprises on the one hand a low-pressure body including the low-pressure compressor CBP, the low-pressure turbine TBP and the first shaft A1, and on the other hand a high-pressure body including the high pressure compressor CHP, the high pressure turbine THP and the second shaft A2. This low pressure body and high pressure body form two rotating assemblies mechanically independent of each other.

When the turbojet engine T is in operation, the primary flow F1 passes first through the low pressure compressor CBP integral with the fan S, then the high pressure compressor CHP. The high pressure compressor CHP channels the compressed fluid to the combustion chamber CC, in which the fluid of the primary stream F1 is mixed with a pressurized fuel. The fluid-fuel mixture is then burned, and the flow exiting the combustion chamber CC drives the high pressure turbine THP. Depending on whether more or less fuel is injected into the DC combustion chamber, the high pressure turbine THP is subjected to variations in speed of rotation.

It will be understood that the combustion chamber CC is arranged, in the direction of fluid flow, between the high pressure compressor CHP and the high pressure turbine THP.

The primary stream F1 is finally ejected at high speed out of the nacelle N towards the rear of the turbojet T by flowing along the CE ejection cone. The ejection of the primary stream F1 at high speed makes it possible to generate a portion of the thrust required for the propulsion of an aircraft.

According to an embodiment of the invention not shown in the figures, the turbojet engine T may also comprise regulating means for regulating the rotational speed of the low-pressure turbine TBP at a substantially constant speed.

When the turbojet engine T is in operation, the fan S is rotated by the passage of the secondary flow F2, which feeds it into the directed towards the rear of the turbojet engine T. The blades and / or the blades of the fan S will interact with the absorbed fluid and increase its speed. The secondary flow F2 flows in the vein V or veins formed inside the nacelle N. The ejection of the fluid corresponding to the secondary flow F2 towards the rear of the turbojet T represents the bulk of the thrust V the propulsion of the aircraft.

By design, a turbomachine is provided to operate within prescribed limits. The compressors of a turbomachine are designed to operate with a sufficient margin, called the pumping margin, so that the turbomachine can operate without pumping in its area of use. It is understood that the capacity of acceleration or deceleration of a turbomachine is limited by this margin to pumping.

It is known, however, that pumping can occur when the operating speed of the low pressure compressor CBP and the speed of the high pressure compressor CHP decrease.

The pumping margin of a low-pressure dual-flow and double-flow T-turbojet compressor CBP depends, among other things, on the air flow therethrough, and on the altitude of the aircraft propelled by this turbojet engine. In particular, this pumping margin is lower for an aircraft flying above a certain altitude, for example 25,000 feet (7620 meters).

A pumping of the low pressure compressor CBP can occur during the flight phase at high altitude of an aircraft. In particular, pumping can occur when the turbojet engine T undergoes a deceleration commanded by the pilot of the aircraft, or by the autothrottle mode in a turbulent atmosphere condition and in particular in the case of a larger headwind . This deceleration leads to a decrease in the respective operating speeds of the low pressure compressor CBP and the high pressure compressor CHP. However, the low pressure compressor CBP is connected to the shaft A1 of the low pressure body, which has more inertia than the shaft A2 of the high pressure body which is connected to the high pressure compressor. The speed of the low pressure compressor CBP thus decelerates less rapidly than that of the high pressure compressor CHP. This results in a pressure rise of the operating line of the low-pressure compressor CBP, especially since the high-pressure compressor CHP has variable-pitch stator vanes which close at deceleration and thus reduce its passage section.

If, during this deceleration, the ratio between the pressure measured at a point situated upstream of the low pressure compressor CBP and the pressure measured at a point situated downstream of the low pressure compressor CBP exceeds a certain threshold, a pumping situation can occur in the low pressure compressor CBP. In this situation, the operation of the turbojet engine T may become unstable, with the consequence of damaging the compressor or other components of the turbojet engine T.

To protect the turbojet T and its various elements, it is known protection devices equipped with VBV discharge valves (acronym for Variable Bleed Valve). As illustrated in FIG. 1 according to one embodiment of the invention, the turbojet engine T comprises VBV discharge valves, for example valves or valves, located between the low pressure compressor CBP and the high pressure compressor CHP.

The VBV discharge valves are designed to evacuate part of the primary stream F1 to the secondary stream F2 when they are open. In particular, the opening of the VBV discharge valves makes it possible to evacuate part of the primary flow F1 passing between the low-pressure compressor CBP and the high-pressure compressor CHP towards the vein V in which the secondary flow F2 circulates. The evacuation of a part of the primary flow F1 in the vein V where the secondary flow F2 circulates makes it possible to protect the turbojet engine T from a pumping of the low-pressure compressor CBP when the latter is traversed by a fluid flow rate greater than that that can accept the high pressure compressor CHP.

Closure of the VBV discharge valves maintains the entire primary stream F1 flowing between the low pressure compressor CBP and the high pressure compressor CHP. VBV discharge valves can be closed, or opened gradually with different possible opening angles. Closing or opening of the VBV discharge valves is controlled by a motor controller according to a predetermined control law, or in response to a particular event. For example, such a control law takes into account the controlled speed of the low pressure compressor CBP, said N1 regime, reduced by a temperature measured at a suitable location of the compressor.

According to one embodiment of the invention, the control law also takes into account data established by a method of detecting conditions conducive to the occurrence of pumping.

According to one embodiment of the invention not shown in the figures, the control of the VBV discharge valves is implemented to prevent the occurrence of a pumping phenomenon in the turbojet engine T when conditions conducive to the appearance of pumping are detected.

With reference to FIG. 2, the steps of the method for detecting conditions conducive to the appearance of pumping according to one embodiment of the invention, when said method is implemented by the turbomachine, are described here.

Here we consider the case of a pump that can affect a low pressure compressor CBP of a turbojet T double body and double flow. It will be understood that this hypothesis is not limiting, and that the invention can also be applied to the high-pressure compressor CHP of a turbojet T, or to other types of aircraft turbomachines.

The detection method comprises a step E1, called the monitoring step, during which at least one parameter of the aircraft, a parameter of the turbojet engine T, a parameter of the high pressure compressor CHP or a parameter of the low pressure compressor CBP is detected.

In addition, a step E2 for detecting an acceleration of the aircraft is implemented when the monitoring step E1 is active. Step E2 evaluates indicators for detecting conditions conducive to the occurrence of pumping, said indicators being, for example, bits set to 1 when they are activated, and to 0 otherwise. These indicators are chosen from at least:

 an indicator iV representative of a variation of speed dV;

 an indicator iN2 representative of a variation of regime dN2.

According to one embodiment of the invention, the steps E1 and E2 are performed simultaneously. Based on statistical and experimental studies of turbomachines of aircraft flying in a turbulent atmosphere, the inventors have been able to determine that the conditions conducive to the occurrence of pumping correspond to two relatively concomitant phenomena:

 a relatively abrupt increase in the speed of the aircraft, and therefore an increase in the Mach number of the aircraft;

 a decrease in the operating speed of the high pressure compressor CHP of the turbomachine.

The variation in speed dV is measured over a predetermined time interval, this time interval being for example equal to 10 seconds, and the variation in speed dV corresponds to an acceleration.

According to one embodiment of the invention, said variation in speed dV of the aircraft is an increase in speed of said aircraft. Said dn2 speed variation of the high pressure compressor CHP is a decrease in the speed of said compressor.

The step E2 for detecting an acceleration of the aircraft comprises a measurement step E10 of a variation of speed dV. Step E2 further comprises a measurement step E20 of a regime variation dN2. Said speed variation dV is an increase in speed of the aircraft, expressed in Mach per second, and said variation in speed dN2 is a decrease in the operating speed of the high pressure compressor CHP, expressed in revolutions per minute per second. According to one embodiment of the invention, a measurement of the speed variation dV is carried out according to the state of the art. This measurement can be performed using probes and / or sensors located on the fuselage of the aircraft, for example on the nose or on the wings. These probes and / or these sensors are configured to measure the flow of air flowing through the aircraft, and include for example a Pitot tube configured to measure the dynamic pressure of the air. The measured dynamic pressure is compared with the static pressure and makes it possible to determine the speed V of the aircraft.

Step E10 measures the speed V of the aircraft in two successive instants, these two successive instants being for example separated by an interval of 10 seconds. In other words, a first speed V1 is measured at a first instant t1, and a second speed V2 is measured at a second instant t2, the second instant t2 occurring 10 seconds after the first instant t1. Step E10 then determines the speed variation dV by calculating the difference V2-V1.

Step E10 compares the speed variation dV with a predefined threshold, said first threshold S1. If said speed variation dV is greater than said first threshold S1, the indicator iV is activated. The value of the indicator iV is set to 1 if a variation of speed dV greater than S1 is detected, and to 0 otherwise. Otherwise, step E10 continues to measure the speed V of the aircraft in order to possibly detect a speed variation dV greater than S1. Step E20 measures at each instant the N2 regime of the high pressure compressor CHP of the turbojet engine T double body and dual flow. Said regime N2 can be measured from the rotational speed of the second shaft A2 of the turbojet T, which mechanically couples the high pressure compressor CHP to the high pressure turbine THP. Step E20 then calculates the regime variation dN2 equal to the derivative with respect to the time of N2 at the corresponding measurement instant.

Step E20 then compares the regime variation dN2 with a negative predefined threshold, said second threshold S2. If said variation of regime dN2 in algebraic value is lower than the second threshold S2 negative, in other words if the absolute value of the regime variation dN2 is greater than a positive predefined threshold which is the absolute value of the second threshold S2, the indicator iN2 is activated. The value of the indicator iN2 is set to 1 if a variation of regime dN2 lower than S2 is detected, and to 0 otherwise. Otherwise, step E20 continues to measure the N2 regime of the high pressure compressor CHP in order to possibly detect a change in regime dN2 less than S2.

According to one embodiment of the invention, step E10 can trigger step E20 when the value of the indicator iV is determined.

The value of the first threshold S1 and the value of the second threshold S2 are chosen so as to allow detection of conditions that are favorable for the occurrence of pumping with a minimum risk of false detection. Said values depend on the operating characteristics of the turbomachine on which the invention is applied.

It was considered the case of an aircraft flying during the flight phase at high altitude. During such a flight of the aircraft, it was observed that:

 - 3% of the average flight time of this aircraft is in a turbulent atmosphere where the speed variations of the aircraft are greater than 0.01

Mach by 10 seconds;

 - 7% of the average flight time of the aircraft takes place in a medium-turbulent atmosphere, where the aircraft speed variations are less than 0.01 Mach for a time interval of 10 seconds and greater than 0.005 Mach for this same time interval;

 - 90% of the average flight time of the aircraft is conducted in a calm atmosphere, where the speed variations of the aircraft are less than 0.005 Mach for a time interval equal to 10 seconds.

Pumping being more conducive to occur in a turbulent atmosphere, the value of the first threshold S1 is thus preferably chosen to be equal to or close to 0.01 Mach per 10 seconds, that is to say 0.001 Mach per second. The Mach of an aircraft flying in high altitude cruising flight phase may correspond to a speed V between 0.74 and 0.80 Mach, a speed between 74% and 80% of the speed of sound.

In addition, for an aircraft in high altitude cruising flight phase, the occurrence of conditions conducive to the occurrence of pumping is necessarily concomitant to a decrease in the operating speed of the turbojet engine HPP high pressure compressor, corresponding to a deceleration, in other words a negative acceleration. This decrease is less than -48 rpm, that is to say higher in absolute value at 48 rpm, over a time interval equal to 10 seconds. The value of the second threshold S2 is thus preferably chosen to be equal to -8 revolutions per minute per second. This value advantageously makes it possible to limit the consequences of erroneous detection of conditions favorable to the occurrence of pumping for a double-body, dual-flow turbojet engine enabling the implementation of the invention.

In particular, it is found that the choice of these values for the thresholds S1 and S2 ensures that under the above-mentioned conditions of turbulent atmosphere, a reduction in the speed of the high-pressure compressor CHP in absolute value to a predefined positive threshold, on a predefined time, will most likely lead to pumping of the low pressure CBP compressor. It has been verified that the detection method limits the erroneous detection of conditions favorable to the occurrence of pumping during decelerations of the speed of the high pressure compressor CHP. On the basis of a statistical study of the flight times of an aircraft equipped with double-body and dual-flow turbojets likely to undergo the aforementioned pumping conditions, the inventors have found that the erroneous detection of pumping conditions in a calm atmosphere and in a moderately turbulent atmosphere only occurred for about 2.5% of the total flight time of the aircraft.

Successively in steps E1 and E2, the detection method comprises a step E5, said stage of detecting conditions conducive to the appearance of a pump, during which the simultaneous activation of the indicators iV and iN2 is examined. If the value of the indicator iV and the value of the indicator iN2 are simultaneously set to 1, conditions conducive to the occurrence of a pumping are detected, and an indicator iP of the pumping hazard is activated. The value of the iP indicator is set to 1 in case of detection of conditions conducive to the occurrence of pumping. Otherwise, the method resumes the monitoring step E1, and continues to monitor the speed variations dV of the aircraft and the dN2 speed variations of the high pressure compressor CHP.

When the conditions conducive to the occurrence of pumping are detected, that is to say when the pumping hazard indicator iP is activated, the detection method may have the function of controlling the opening of the pumping valves. VBV discharge to protect the turbine engine T from pumping.

As illustrated in FIGS. 3, 4 and 5, other indicators than the iV and iN2 indicators can be used to reinforce the reliability of the detection of conditions conducive to the occurrence of pumping. According to one embodiment of the invention as illustrated in FIG. 3, the detection method comprises a step E3, called the high altitude detection step. This step E3 for detecting a high altitude can be implemented substantially simultaneously or successively in step E2 when the monitoring step E1 is active.

According to one embodiment of the invention, the step E3 comprises a preliminary measurement step E30 during which an altitude A of the aircraft is measured. This measurement of an altitude can be performed using an altimeter located on the fuselage of the aircraft.

The preliminary step E30 compares, at each instant, the altitude A of the aircraft to a predefined threshold, said third threshold S3. If said altitude A of the aircraft is greater than said third threshold S3, the indicator iA is activated. The value of the indicator iA is set to 1 if an altitude A greater than S3 is detected, and to 0 otherwise. Otherwise, the preliminary step E30 continues to measure the altitude A of the aircraft with a view to possibly detecting an altitude greater than S3.

Successively in the steps E1, E2 and E3, the detection step E5 examines the simultaneous activation of the indicators iA, iV and iN2. If the values of these indicators are simultaneously set to 1, the conditions conducive to the occurrence of pumping are detected and the pumping hazard indicator iP is activated. In particular, the indicator iP is set to 1. Otherwise, the method resumes the monitoring step E1, and continues to examine the variations in speed of the aircraft, the variations in the speed of the high-pressure compressor and the altitude of the aircraft.

According to one embodiment of the invention as illustrated in FIG. 4, the detection method may also comprise a step E4, said stage of detection of an engine deceleration. This step E4 for detecting an engine deceleration can be implemented substantially simultaneously or successively to the steps E2 and E3 when the monitoring step E1 is active.

The step E4 for detecting an engine deceleration comprises a measurement step E40 of a first speed N1, called the controlled speed of the low pressure compressor CBP. In addition, the step E4 includes measuring step E50 of a second regime N1 \ said current regime of the low pressure compressor CBP.

For an aircraft in the cruising flight phase, it is important to distinguish the controlled speed from the current speed of a turbomachine T. The controlled speed N1 corresponds to the operating speed of the low pressure compressor CBP required by the pilots of the aircraft when they control the turbine engine T each using a throttle. The current regime N1 'corresponds to the actual operating speed of the low pressure compressor CBP. Because there is always a response time between the throttle controlled regime and the current regime of the low pressure compressor CBP, the regimes N1 and N1 'are not always equal.

Based on the measurement of the controlled speed N1 and the measurement of the current regime NT, step E4 then measures the difference between these two values at each instant. The difference between N1 and NT, equal to N1 - N1 \ is then compared to a predefined threshold, said fourth threshold S4. If the difference N1 - N1 'is lower than said fourth threshold S4, the indicator iN1 is activated. The value of the indicator iN1 is set to 1 if a difference in speed below S4 is detected, and to 0 otherwise. Otherwise, steps E40 and E50 continue to monitor the controlled speed N1 and the current regime NT for possible detection of a speed difference below S4.

In auto-joystick mode, and since the controlled deceleration is slow at high altitude in the event of a sharp Mach increase, the difference between the current speed N1 'and the controlled speed N1 may be less than the detection threshold S4 throughout. deceleration, which leads to not detect it, hence the need to implement a second logic.

Successively in the steps E1, E2, E3 and E4, the detection step E5 examines the activation of the indicators iA, iV and iN2. If the values of these indicators are simultaneously set to 1, the conditions conducive to the occurrence of pumping are detected and the pumping hazard indicator iP is activated. In particular, the indicator iP is set to 1. Otherwise, the method examines the activation of the indicator iN1. If the indicator iN1 is set to 1, conditions conducive to the occurrence of pumping are detected. Otherwise, the method resumes the implementation of the monitoring step E1, and continues to monitor the speed variations of the aircraft, the speed variations of the high pressure compressor CHP, the altitude of the aircraft, and the RPM variations of the CBP low pressure compressor. The value of the fourth threshold S4 is chosen so as to allow a detection of conditions favorable to the appearance of a pump when the aircraft flies in auto-joystick mode.

Controlled regime N1 'remaining constant in auto-joystick mode, conditions conducive to the occurrence of pumping can be detected when the difference between N1 and N1' becomes less than -1000 revolutions per minute over a period of time. 10 seconds. The value of the fourth threshold S4 is thus preferably chosen to be equal to -100 revolutions per minute per second. According to this embodiment, it is possible to detect a pumping from the detection of a decrease in speed V of the aircraft, a variation dN2 of the operating speed of the high pressure compressor CHP, a detection of a high altitude A of the aircraft and a detection of a difference between controlled speed N1 and current regime N1 'of the low pressure compressor CBP. When the steps E1, E2, E3, and E4 are implemented, a reliable and accurate detection of conditions conducive to the occurrence of pumping that can affect a double-body and dual-flow turbojet T is feasible at high altitude and at low altitude. According to another embodiment of the invention not shown in the figures, these steps can be implemented for several turbomachines. In addition, these steps can be implemented for different turbomachines.

With reference to FIG. 5, the invention also aims at a device DD for detecting conditions that are favorable for the appearance of a pumping, this pumping being able to affect a low-pressure compressor CBP of a turbomachine, this turbomachine further comprising a compressor high pressure CHP.

The device DD for detecting conditions conducive to the occurrence of pumping is activated by the monitoring step E1 by a monitoring device DS. In addition, the device DD for detecting conditions conducive to the onset of pumping controls a device DO for opening the VBV discharge valves.

According to one embodiment of the invention, the device DD comprises:

 first measuring means M10, for example including a speed sensor, configured to measure a speed V and to calculate a speed variation dV of said aircraft during the step E10;

 second measuring means M20, for example including a speed variation sensor, and configured to measure a variation of the speed dN2 of the high pressure compressor CHP during the step E20.

The device DD also comprises means for implementing the step E2 and thus activating the indicators iV and iN2 from the comparison of the speed variation dV and the speed variation dN2 of the high pressure compressor CHP at the first threshold S1 and the second threshold S2, respectively.

The device DD further comprises:

 third measurement means M30, for example including an altitude sensor such as an altimeter, configured to measure an altitude A of the aircraft during the preliminary step E30;

 fourth measurement means M40, including for example an aircraft control system, configured to measure a controlled speed N1 of the low pressure compressor CBP during the step E40;

 fifth measurement means M50, including, for example, a speed sensor capable of measuring the rotational speed of the shaft A1, configured to measure a current regime N1 'of the low pressure compressor CBP during the step E50.

The device DD further comprises means for implementing the step E3 and activating the indicator iA from the comparison of the altitude A with a third threshold S3. When conditions conducive to the occurrence of pumping are detected, i.e. when the pumping hazard indicator iP is turned on, the opening device VBV discharge opening DO is commanded to open said discharge valves. A method and a detection device according to one or the other embodiment of the invention makes it possible to open the VBV discharge valves when detecting conditions conducive to the occurrence of pumping.

FIG. 6 represents a graph illustrating an example of variation of several parameters when a pumping appears in a turbomachine. These parameters are here the speed V of the aircraft, more particularly its Mach, the operating speed N2 of the high pressure compressor CHP, and an indicator iP representative of the detection of conditions conducive to the appearance of a pump when method according to one embodiment of the invention is implemented. The variations of the three parameters V, N2 and iP are represented over a time interval of between 250 seconds and 300 seconds. The speed V of the aircraft and the operating speed N2 of the high pressure compressor CHP are measured at the same interval.

The speed V of the aircraft increases from 0.755 Mach to 0.77 Mach between 250 seconds and 275 seconds, then decreases from 0.77 Mach to 0.76 Mach from 275 seconds to 300 seconds. The operating speed N2 decreases from 1620 rpm to 1580 rpm from 250 seconds to 275 seconds and then increases from 1580 rpm to 1590 rpm from 275 seconds to 300 seconds.

As illustrated, the invention makes it possible to detect conditions that are favorable for the occurrence of a pumping between the instant t1 of 258 seconds and the instant t2 of 268 seconds. Indeed, a speed V equal to 0.76 Mach is measured at time t1. At time t2, a speed V equal to 0.77 Mach is measured. The difference in speed dV observed in the interval of 10 seconds between the instant t1 and the instant t2 is therefore equal to 0.01 Mach. The indicator iV is activated in this case, signaling a speed increase dV greater than the first threshold S1, this first threshold being fixed in this example at 0.009 Mach over a period of 10 seconds, an acceleration threshold of 0.0009. Mach per second. In addition, a regime N2 equal to 16150 revolutions per minute is measured at time t1, and a regime N2 equal to 16000 revolutions per minute is measured at time t2. The diode difference dN2 in the interval of 10 seconds between the instant t1 and the instant t2 is equal to -150 revolutions per minute, that is to say equal to -15 revolutions per minute per second, and is therefore less than -8 revolutions per minute per second. The indicator iN2 is activated in this case, signaling a decrease in the operating speed of the high pressure compressor CHP lower than the threshold S2. The indicator iV and the indicator iN2 being positioned at 1 between time t1 and time t2, the indicator iP representative of the detection of conditions conducive to the occurrence of pumping is also activated on this interval. It will be understood that a method for detecting conditions conducive to the occurrence of pumping according to one of the embodiments of the invention described herein, as well as a pumping detection device according to this embodiment, is implemented in a turbomachine. In particular, the turbomachine may be a turbojet T double body and dual flow, comprising the device DD for detecting conditions conducive to the occurrence of a pump.

According to one embodiment of the invention, the device DD for detecting conditions conducive to the appearance of a pump is implemented using software implemented in an electronic control unit of the turbomachine, on board on the turbomachine, called ECU (Engine Control Unit) or also FADEC (Full Authority Digital Engine Control). In particular, this software includes instructions adapted to the implementation of any step of the method described above.

Claims

Claims 1. A method of detecting conditions conducive to the occurrence of pumping that can affect a low pressure compressor (CBP) of an aircraft turbomachine, said turbomachine further comprising a high pressure compressor (CHP), said method being characterized in what he understands:  a first measurement step (E10) of a speed variation (dV) of said aircraft;  a second measurement step (E20) of a variation in speed (dN2) of said high pressure compressor (CHP);  a preliminary measurement step (E30) of an altitude (A) of the aircraft; the conditions conducive to the occurrence of pumping being detected when the following conditions a), b) and c) are performed jointly: a) said variation in speed (dV) measured over a predetermined time interval corresponds to a higher acceleration at a first threshold (S1) positive, and  b) said measured variation in speed (dN2) corresponds to a deceleration lower than a second negative threshold (S2);  c) said measured altitude is greater than a predetermined third threshold (S3). 2. The detection method according to claim 1, characterized in that said first threshold (S1) is between 10 ^-4 Mach per second and 10 ^-2 Mach per second, the first threshold being for example equal to 0.001 Mach per second . 3. The detection method according to any one of claims 1 or 2, characterized in that said time interval is between 3 seconds and 20 seconds, the time interval being for example equal to 10 seconds. 4. The detection method according to any one of the preceding claims, characterized in that said second threshold (S2) is between -2 revolutions per minute per second and -20 revolutions per minute per second, the second threshold being for example equal to -8 revolutions per minute per second. 5. The detection method according to any one of the preceding claims, characterized in that said third threshold (S3) is between 20000 feet (6096 meters) and 30000 feet (9144 meters), the third threshold being for example equal to 25000 feet (7620 meters). The detection method according to any one of the preceding claims, characterized in that said method further comprises:  a fourth measuring step (E40) of a first controlled speed (N1) of the low pressure compressor (CBP);  a fifth measurement step (E50) of a second current regime (Ν1 ') of the low pressure compressor (CBP);  the conditions conducive to the occurrence of pumping being detected, independently of the fulfillment of conditions a), b) and c), when the following condition d) is realized:  d) the difference between said first measured controlled speed (N1) and said measured second current regime (NT) is less than a fourth threshold (S4), said fourth threshold being for example equal to -100 revolutions per minute. 7. The detection method according to claim 6, characterized in that if the measured altitude is lower than the third threshold (S3), the first and second measurement steps (E10, E20) are ignored and the conditions favorable to the pumping is detected when condition d) is performed. 8. The detection method according to any one of the preceding claims, characterized in that the detection of conditions conducive to the occurrence of pumping triggers an opening control of discharge valves (VBV) located between the low compressor pressure (CBP) and the high pressure compressor (CHP). 9. The detection method according to any one of the claims  preceding,  characterized in that said variation of regime (dN2) is measured by calculating the derivative (dN2 / dt) of the regime and then filtering it with a time constant adapted to average the measurement over a time interval between 1 second and 3 seconds. 10. A device for detecting conditions conducive to the occurrence of pumping which can affect a low pressure compressor (CBP) of an aircraft turbomachine, said turbine engine further comprising a high pressure compressor (CHP), said device being characterized in that it comprises:  first measuring means (M10) of a speed variation (dV) of said aircraft;  second measurement means (M20) of a variation in speed (dN2) of said high pressure compressor (CHP);  third measurement means (M30) of an altitude (A) of the aircraft;  the device further comprising means for detecting an acceleration of the aircraft, said detection means comprising:  means for activating a first indicator (iV) representative of a speed variation;  means for activating a second indicator (iN2) representative of a variation in the speed of the high pressure compressor (CHP); means for activating a third indicator (iA); - Means for activating a pumping risk indicator (iP) representative of the detection of conditions conducive to the onset of pumping;  said pump hazard indicator (iP) being activated when the first indicator (iV), the second indicator (iN2) and the third indicator (iA) are activated simultaneously;  the first indicator (iV) being activated when the variation in speed (dV) measured over a predetermined time interval corresponds to an acceleration greater than a first threshold (S1);  the second indicator (iN2) being activated when the measured variation in speed (dN2) corresponds to a deceleration lower than a second threshold (S2); and  the third indicator (iA) being activated when the measured altitude is greater than a predetermined third threshold (S3). 11. The detection device according to claim 10, characterized in that said first threshold (S1) is between 10 ^-4 Mach per second and 10 ^-2 Mach per second, the first threshold being for example equal to 0.001 Mach per second. . 12. The detection device according to any one of claims 10 and 11, characterized in that said time interval is between 3 seconds and 20 seconds, the time interval being for example equal to 10 seconds. 13. The detection device according to any one of claims 10 to 12, characterized in that said second threshold (S2) is between -2 revolutions per minute per second and -20 revolutions per minute per second, the second threshold being for example equal to -8 revolutions per minute per second. 14. The detection device according to any one of claims 10 to 13, characterized in that said third threshold (S3) is between 20000 feet (6096 meters) and 30000 feet (9144 meters), the third threshold being for example equal to 25000 feet (7620 meters). 15. The detection device according to any one of claims 10 to 14, characterized in that said device further comprises:  fourth measurement means (E40) of a first controlled speed (N1) of the low pressure compressor (CBP);  fifth measurement means (E50) of a second current regime (NT) of the low pressure compressor (CBP);  the means for detecting an acceleration of the aircraft further comprising means for activating a fourth indicator (iN1), the pumping hazard indicator (iP) being activated when the first indicator (iV), the second indicator (iN2) and the third indicator (iA) are not activated simultaneously and when said fourth indicator (iN1) is activated, said fourth indicator (iN1) being activated when the difference between said first controlled speed (N1) measured and said measured second current regime (NT) is less than a fourth threshold (S4), said fourth threshold being for example equal to -100 revolutions per minute. 16. Aircraft turbomachine comprising the detection device according to any one of claims 10 to 15.